In general, the integration of a flexible, electrically conductive element within the structure of a hose for transfer of fluids, has been used as a method of dissipating static electricity charges. For example, it is well known that gasoline and other hydrocarbon liquids generate static electricity when flowing through a rubber lined hose, and that this has been the direct cause of many disastrous explosions and fires originating at filling stations. Since an automobile is supported on rubber tires, which are good electrical insulators, the static electricity that has built up in and around the hose, instead of escaping to the ground as it should when the hose contacts the automobile, merely charges the automobile chassis and body, which then serves as an enormous condenser. The capacity for storing charge in the automobile body and chassis is large, and the electrical potential thus does not rise sufficiently during the tank filling operation to cause a spark to jump from the wheel rims to the ground, as the gap there is excessively great. It happens, however, that the static charge that accumulates during the time the tank is being filled is sufficient to cause a spark when a person standing on the ground moves his fingers towards the conducting portions of the car body. If this spark takes place at or near the filling opening, it is sometimes enough to ignite the inflammable and explosive vapors that are given off from the gasoline.
As another example, hoses and tubes that carry volatile anesthetics used in surgical procedures, are likewise subject to this build-up of static electricity. Unless the static electricity is conducted along the hose or tube to grounding means, it can build up sufficient potential to cause a spark to form, igniting the highly volatile anesthetic vapors.
In general, the types of electrical charges or signals described above have been conducted along hoses or tubes through the use of plastic or rubber elastomers, which have been made semiconductive by the inclusion of particles of carbon that have been embedded in the structure of the elastomer. Another general approach has been to use metallic wires, which have been braided or spirally or helically wound around at least a portion of the hose or tube. Another approach has been to assemble a wire braid, then flatten the braid out so as to form a ribbon, and then lay the ribbon so as to follow the length of the hose or tube.
In those instances where the electrical charge or signal that was being conducted was generated by static electricity, it was also necessary to find some way of connecting the electrical conductor to an electrical grounding means. Generally, this meant that some sort of multiple pronged plate or circular ring was inserted into an end of the hose or tube so as to contact the electrically conductive portion on one end, and so as to contact with a hose coupler that was generally metallic. The hose coupler was then electrically attached to a ground.
When electrical conductors were comprised of plastic which had been made electrically conductive, the plastic would generally lose the aesthetic qualities which were sought in using the plastic in the first place. Furthermore, under some circumstances, in very high pressure hoses such as in aircraft applications, the formation of a microspark could cause a pinhole within the hose resulting in a rupture and failure of the hose. (Rowand, U.S. Pat. No. 3,166,688). On the other hand, use of electrically conductive rubber sometimes results in a heat build-up accompanying the conduction of static electricity. This heat build-up on occasion would be sufficient to ignite the hose. (Bulgin, U.S. Pat. No. 2,341,360). The use of metallic electrical conductors presented their own problems. Since they would have to be braided spirally or helically wound or zigzagged into the construction in order to impart flexibility to the finished product, these intricate methods of application would result in slow production speeds and increased production costs. A particular problem was that, due to the high flexural modulus of metallic wire, it would have a tendency to break during repeated flexing, which then would cause a loss of electrical conductivity.
There is, therefore, a need in the art for a hose and a method for producing hose, which overcomes these deficiencies. Thus, an initial object of the invention is to provide a hose product and a method of making it that uses a nonmetallic electrical conductor capable of conducting static electricity charges so as to prevent the accumulation of those charges in the area of the hose. The hose should be relatively inexpensive to manufacture, while the conductive member itself should be highly resistant to fatiguing and breaking under conditions of repeated flexing and bending. It will logically be appreciated that another object of the invention is to place a simple, inexpensive, reliable, nonmetallic, electrical conductor within the body of a hose or tube for the purpose of conducting electrical charges other than static electricity charges. A further object of the invention is to provide a simple and inexpensive means for electrically connecting the nonmetallic electrical conductor in the hose or tube to a hose coupling device. It is yet a further object of the invention to provide a hose or tube article having a photoconductive member included in the body of the tube or hose, for example, strands of fiber optics.